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Ming-Hung Tsai
0c5eef0aad
In passthrough mode, dm-cache defers write bio submission until cache
invalidation completes to maintain existing coherency, requiring the
target map function to return DM_MAPIO_SUBMITTED. The current map_bio()
returns DM_MAPIO_REMAPPED, violating the required ordering constraint.
Reproduce steps:
1. Create a cache device
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 131072 linear /dev/sdc 8192"
dmsetup create corig --table "0 262144 linear /dev/sdc 262144"
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache --table "0 262144 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
2. Promote the first data block into the cache
fio --filename=/dev/mapper/cache --name=populate --rw=write --bs=4k \
--direct=1 --size=64k
3. Reload the cache into passthrough mode
dmsetup suspend cache
dmsetup reload cache --table "0 262144 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 passthrough smq 0"
dmsetup resume cache
4. Write to the first data block, and check io ordering using ftrace
echo 1 > /sys/kernel/debug/tracing/events/block/block_bio_queue/enable
echo 1 > /sys/kernel/debug/tracing/events/block/block_bio_complete/enable
echo 1 > /sys/kernel/debug/tracing/events/block/block_rq_complete/enable
fio --filename=/dev/mapper/cache --name=test --rw=write --bs=64k \
--direct=1 --size 64k
5. ftrace logs show that write operations to the cache origin (252:2)
and metadata operations (252:0) are unsynchronized: the origin write
occurs before metadata commit.
<snip>
fio-146 [000] ..... 420.139562: block_bio_queue: 252,3 WS 0 + 128 [fio]
fio-146 [000] ..... 420.149395: block_bio_queue: 252,2 WS 0 + 128 [fio]
fio-146 [000] ..... 420.149763: block_bio_queue: 8,32 WS 262144 + 128 [fio]
fio-146 [000] dNh1. 420.151446: block_rq_complete: 8,32 WS () 262144 + 128 be,0,4 [0]
fio-146 [000] dNh1. 420.152731: block_bio_complete: 252,2 WS 0 + 128 [0]
fio-146 [000] dNh1. 420.154229: block_bio_complete: 252,3 WS 0 + 128 [0]
kworker/0:0-9 [000] ..... 420.160530: block_bio_queue: 252,0 W 408 + 8 [kworker/0:0]
kworker/0:0-9 [000] ..... 420.161641: block_bio_queue: 8,32 W 408 + 8 [kworker/0:0]
kworker/0:0-9 [000] ..... 420.162533: block_bio_queue: 252,0 W 416 + 8 [kworker/0:0]
kworker/0:0-9 [000] ..... 420.162821: block_bio_queue: 8,32 W 416 + 8 [kworker/0:0]
<snip>
Fixes: b29d4986d0 ("dm cache: significant rework to leverage dm-bio-prison-v2")
Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
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